.supports now also uses cache

Author: sobolevn

classes/_typeclass.py

@@ -480,11 +480,20 @@ def supports(
 
         See also: https://www.python.org/dev/peps/pep-0647
         """
+        self._control_abc_cache()
+
         instance_type = type(instance)
-        return (
-            instance_type in self._dispatch_cache or
-            self._dispatch(instance, instance_type) is not None
-        )
+        if instance_type in self._dispatch_cache:
+            return True
+
+        # This only happens when we don't have a cache in place:
+        impl = self._dispatch(instance, instance_type)
+        if impl is None:
+            self._dispatch_cache[instance_type] = self._default_implementation
+            return False
+
+        self._dispatch_cache[instance_type] = impl
+        return True
 
     def instance(
         self,

tests/test_suppots.py

@@ -0,0 +1,36 @@
+from typing import Sized
+
+import pytest
+
+from classes import typeclass
+
+
+@typeclass
+def my_len(instance) -> int:
+    """Returns a length of an object."""
+
+
+@my_len.instance(Sized, is_protocol=True)
+def _my_len_sized(instance: Sized) -> int:
+    return 0
+
+
+@my_len.instance(list)
+def _my_len_list(instance: list) -> int:
+    return 1
+
+
+class _MyList(list):  # noqa: WPS600
+    """We use it to test mro."""
+
+
+@pytest.mark.parametrize(('data_type', 'expected'), [
+    ([], True),  # direct list call
+    ('', True),  # sized protocol)
+    (1, False),  # default impl
+    (_MyList(), True),  # mro fallback
+])
+def test_supports(data_type, expected):
+    """Ensures that ``.supports`` works correctly."""
+    assert my_len.supports(data_type) is expected
+    assert type(data_type) in my_len._dispatch_cache  # noqa: WPS437, WPS516